Historically, the automotive industry has used colored plastic lenses over white light generating bulbs to produce an output light signal having a desired chromaticity or objective specification of the quality of a color regardless of its luminance so as to maximize visibility and illumination characteristics without unduly interfering with the function of the eye of the viewer. The performance of plastics associated with such light devices is governed by regulations promulgated by various agencies such as the U.S. Department of Transportation Federal Motor Vehicle Safety Standard (FMVSS) 108, the UN European standard, etc. The entirety of which are expressly incorporated herein. The result of such regulations has been the availability of only limited materials for automotive lighting lens applications. Developing of and seeking approval for new lens materials is commonly a costly and time intensive process.
One such body that has been delegated responsibility associated with maintaining desired vehicle marker lighting visibility is the Automotive Manufacturers Equipment Compliance Agency, Inc. (AMECA) of Washington D.C. AMECA periodically publishes a listing of “Acceptable Plastics for Optical Lenses and Reflex Reflectors Used on Motor Vehicles.” The fall 2005 and October 2014 Final Edition of the “Acceptable Plastics for Optical Lenses and Reflex Reflectors Used on Motor Vehicles” AMECA publication is expressing incorporated herein as disclosing various acceptable materials for use as motor vehicle optical lenses and reflex reflectors. Still other bodies, such as the American Boat and Yacht Council, Inc. (ABYC) and the American National Standards Institute (ANSI) have developed various equipment division standards, such as the Equipment Division Standard Navigation Lights and Sound Signal Appliances Project Technical. Committees, (ABYC A16, July 2011) associated with designating suitable standards for Electrical Navigation Lights as well as the Jun. 3, 2013 International Organization for Standards (ISO) New Work Proposals for Performance and Testing of LED Navigation Lights which promulgate international requirements for marine navigation light performance. The disclosures of each of which are expressly incorporated herein.
Further limiting industry choices, incandescent bulbs used in developing red, yellow, green and blue lighting with the correct filtering have functionally similar output spectra which follow very closely to the Planck blackbody emission spectrum which associates a radiation spectrum, intensity, and temperature of the respective body. The result of these two situations is an extremely limited choice of available lighting and filtering materials that can satisfy the regulatory performance requirements to provide the desired spectral characteristics. For instance, when designing a lighting fixture to satisfy automotive requirements, specifying a certified plastic having the automotive red or amber color from different manufacturers can result in nearly imperceptible difference in color performance between the lenses when placed over the same light sources, thereby rendering any choice between different manufacturers or different automotive certified lens plastics nearly irrelevant to the color performance of a given lamp.
In recent years, solid state illumination devices such as light emitting diodes (LED's) have gained popularity in use in various applications including the automotive markets, due in no small part to the efficiency with which such devices generate light from electrical energy. Although efficient at generating light from an electrical signal, such devices commonly generate light energy having characteristics that are ill-suited for many applications, absent some manipulation of the light signal, and still other applications suffer from drawbacks associated with the integration, of the illumination device into the operating systems associated with an underlying device.
For instance, amber aluminium indium gallium phosphide (AlInGaP) LED technologies in automotive lighting applications have problems related to the generation of heat during operation. Such LED's have the advantage of directly generating light output of a narrow spectral range in only the color needed. Standard colored plastics from the automotive industry transmit well in the wavelength range of these LED's and therefore do not or only negligibly affect the spectral output of the devices. However, the generation of heat in the die during operation of such LED's causes color shifting of the output which creates problems in meeting government standards for color and visibility, such as the UN defined European and U.S. vehicle safety specifications. Another significant concern, particularly for amber LED's, is a substantial intensity drop that occurs during operation of the device. Amber die LED technology exhibits up to a 50% loss of output as the temperature of the device transitions from start-up to steady state conditions. Such a deviation results in a color shift in AlInGaP LED devices which are bright yellow upon startup but quickly shift to a dimmer redder light. The AlInGaP LED color and brightness problems have prevented production of otherwise cost effective solutions since the beginning of the automotive LED lighting technology.
Indium gallium nitride (InGaN) type LED's have only more recently been developed and commonly use phosphor materials to create a wide spectrum white light output. The vehicle signal lighting potential of this technology has yet to garner appreciable interest from LED manufacturers for the direct production of vehicle approved phosphor red, green, blue or amber light derived from the high energy blue/blue green or UV light generated by InGaN type LED's. The difficulties in amber AlInGaP LED performance have resulted in a number of phosphor based amber solutions. Commonly, InGaN die and phosphor combinations are manufactured to convert short wavelength blue or ultraviolet light into the other components of the desired spectrum as phosphors placed near the die absorb the shorter, higher energy, wavelengths and generally re-emit at longer wavelengths. Through chemistry, the output can typically be fine-tuned to white light having a more complete spectrum or it can be tuned to other colors such as amber. Such customized developments substantially increase the cost associated with the production of each discrete light however basic, characteristics of the InGaN die-phosphor combination can produce a dramatically reduced color shift during warm-up with minimal intensity loss or droop during warm-up.
In an attempt to resolve the most severe color and brightness shortcomings of LED based amber light sources, some LED manufacturers have begun producing InGaN LED lights that provide a yellow output to satisfy the color coordinates associated with vehicle lighting industry requirements. The table below includes various color coordinate values associated with the generation of desired light colors. Although there has been some acceptance of such technologies in limited industries, the relatively low cost of AlInGaP LED technology has traditionally outweighed the cost and complexity associated with implementation of the phosphor based lighting and color solutions in many applications and with the ability to achieve an illumination parameter at prescribed color coordinates.
Signallight colourCoordinates of the verticesWhiteX0.3100.4430.5000.5000.4530.310y0.2830.3820.3820.4400.4400.348RedX0.6900.7100.6800.660y0.2900.2900.3200.320GreenX0.0090.2840.2070.013y0.7200.5200.3970.494YellowX0.6120.6180.5750.575y0.3820.3820.4250.406BlueX0.1360.2180.1850.102y0.0400.1420.1750.105
Unlike current automotive LED technology, white LED's have high competition in markets like interior lighting, video screen backlighting, and commercial lighting. Television manufacturing companies have also begun producing LED devices rather than rely on outside suppliers and have begun offering their devices for sale commercially. Price and performance pressures have mounted across the industry as many large manufacturers have entered the field. Unfortunately, such white light LED technologies are ill-suited for use in many known vehicle lighting systems.
As alluded to above, when designing for automotive lighting requirements, specification of a certified plastic materials having a desired automotive red or amber color from different manufacturers results in very similar color performance when placed over an incandescent or halogen light source such that choice of manufacturer or different automotive certified plastic supplier is nearly irrelevant as to the underlying performance of the resultant lamp. In addition, efficiency pressures in the industry demand that today's white light LED's produce a white light output which does not exactly follow Planck's blackbody spectral curve and typically produces very little long-wavelength red light. High performance white light LED's are rated in Lumens; an eye response weighted measure of light output. One Lumen of green is equally as bright as one Lumen of blue, but the human eye does not respond to blue as strongly as green such that the one Lumen of blue will actually have more radiance (watts) than the one Lumen of green. Also important to visual inspection of such lighting devices is attention to characteristics related to the physical response of the human eye to the light, such as the ability of the human eye to be stimulated to perceive white with as few as two monochromatic wavelengths although three monochromatic wavelengths are commonly used in other industries such as the television industry.
Typically, manufacturers of LED illumination devices, in an effort to maximize performance of the LED device, tailor their products to maximize the generation of light within the spectrum where the human eye is most efficient. Unfortunately, and detrimentally for vehicle applications, the human eye is less efficient at perceiving the deep red light spectrum, such that white light LED manufacturers tailor their products to limit the production of the longer wavelengths of red light to favor the higher performance yet perceivably white light LED's.
The color rendering index (CRI) is another consideration that must be assessed when LED's are utilized for illumination. The CRI of an LED is a typical measure of color quality. A value of 100 represents a perfect color match to the blackbody curve. Incandescent lamps have a CRI value that approaches 100 such that they generate outputs that very nearly match the blackbody curve but fluorescent lamps typically have a CRI of about 50. In order to achieve a high CRI, in practice, all colors must be produced to some extent by a respective lighting device. Unfortunately, many of the high CRI LED devices still do not produce sufficient red to produce light of a chromaticity within the automotive color requirements using commercially available and acceptable automotive lens plastics. The result of these paradigms is an inability of prior art assemblies to utilize white LED's to produce an amber or red light that satisfies the regulated lighting requirements and utilizes any of the commercially available filtered yellow and/or red lenses. Accordingly, there is a need for a white light based LED vehicle fixture which can satisfy externally dictated structure and illumination requirements.
Therefore, it is desirable to produce an LED based vehicle light having reduced warm-up induced color shift and intensity loss, that can be manufactured in a cost-effective manner, can produce a brighter light than other known lighting devices that satisfy the regulatory requirements, and can be provided in a relatively compact form factor and have sufficient intensity and color characteristics to meet one or both of American and/or European vehicle industry lighting or illumination color and output specifications. As used herein, it is appreciated that the vehicle industry includes various methods of conveyance or transportation such that use of the terms “vehicle” or “vehicle industry” includes various different types of vehicles that operate in different environments and includes automotive, marine, emergency, recreation, aviation vehicles, etc. It is appreciated that such terms connote an intended use of the vehicle, an operating environment, and other features that may be specific or common between the respective vehicle types. The present invention is applicable to various “vehicle” configurations.